This invention generally relates to a method and apparatus for recording and reproducing digital data and more particularly relates to the recording and reproducing of digital data onto and from a magnetic tape.
Various arrangements have been suggested and described for the temporary storage of digital information. A particular storage media enjoying increased interest is a magnetic tape. Such tapes are conveniently stored in small enclosed cassettes. An apparatus particularly adapted for recording and playback of digital signals from such magnetic tape cassettes is described in a copending application of K. Rothlisberger and R. Vee, Ser. No. 479,395, filed June 14, 1974, entitled "Apparatus and Method for Positioning A Tape Cassette," having a common assignee herewith. One problem frequently encountered with the use of magnetic tape cassettes is that noise levels during playback tend to be high, often causing the generation of erroneous data signals. The maximum recording speed at which such magnetic tape cassettes can be utilized has been limited by the mechanical problems encountered in handling the tape at high speeds. Further, aside from the mechanical problems encountered with high recording speeds, pulse crowding upon the tape at higher bit densities results in lower signal levels during playback making the playback system more susceptible to noise problems.
Different detection systems have been utilized during playback for sensing the flux reversals on the tape as created by the recording signal. These systems have generally been rather complicated and have often utilized a circuit tuned to a particular digital data frequency and bit density. However, when the recording signal changes or the tape speed materially varies, as is the case with direct reel rather than capstan drive of the tape, the detector tuned circuit requires readjustment for optimum performance. The following described embodiment includes means for effectively increasing the data density carried by a magnetic tape without an increase in the mechanical speed at which the tape is transported nor with a resulting increase in the bit density of the recorded signal. Additionally, the described embodiment includes improved means for detecting the data signal recorded upon a magnetic tape which is relatively free from the adverse effects of system noise.